This invention relates generally to a technique for delivering drugs and/or chemicals, and, more particularly, to effecting such delivery by using nonionizing electromagnetic fields (microwave and RF radiation) to release drugs from liposomes by nonthermal means.
It has been well recognized in the medical field that one of the most effective procedures in treating localized disease is to direct the treatment of that disease directly to the affected area. Some techniques in use today to deliver drugs within the body involve the utilization of time-released capsules in which drugs slowly "leak" from the capsule, or implantable "syringes" that mechanically release drugs into muscles or the blood stream. Another, and perhaps more effective delivery system, encompasses the use of liposomes containing the appropriate drug and/or chemical. The liposome encapsulated drug is then directed to the specific area of interest and the drug released. This last stop is the most problematic. Liposomes are microscopic particles which are made up of one lipid bilayer enclosing a single aqueous compartment. They are normally not leaky but can become leaky if a hole occurs in the membrane, if the membrane is dissolved or degrades, or if the membrane temperature is increased to the phase transition temperature T.
Unfortunately, as pointed out in an article by Milton B. Yatvin et. al., "Design of Liposomes for Enhanced Local Release of Drugs by Hyperthermia," Science, vol. 202, Dec. 22, 1978, pp 1290-1292, the major barrier to the use of liposomes as drug carriers is making the liposomes release the drugs at target sites. In both the above-identified article by Milton B. Yatvin et. al. and an article by J. N. Weinstein et. al., "Liposomes and Local Hyperthemia: Selective Delivery of Methotrexate to Heated Tumors," Science, vol. 204, Apr. 13, 1979, pp 188-191, the specific use of heat to raise liposome temperature to T.sub.c to make them leaky is described.
The technique as presented above still falls short as an effective drug release technique since the prolonged application of heat can, in itself, create problems within the human body, and in many instances drug release by significant liposome heating may damage body tissues to such an extent that the adverse effects of the treatment outweigh the beneficial effects of the drug being released. Therefore, the need for an effective system in which chemicals/drugs are released from liposomes without the need for heating is an important major problem in the medical industry.